Removal of hf from hf-oil and oil-hf solutions



Patented Dec. 5, 1950 REMOVAL OF HF FROM HF-OIL AND OIL-HF SOLUTIONS Waldemar R. Hertwig, Whiting, and James D.

Bushnell, Hammond, Ind., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana Application December 13, 1947, Serial No. 791,646

3 Claims.

This invention relates to removal of HF from HF-oil and oil-HF solutions and it pertains more particularly to improvements in the HF recover} portion of an HF-oil treating system such, for example, as a system for extracting a gas oil with HF for removing sulfur compounds and carbonforming components.

The invention is applicable to systems for the HF extraction of gas oils, particularly to cracked gas oils such as coke still gas oil and catalytic cycle gas oil, and it may also be applicable to other HF treating systems wherein HF must be separated from an HF-oil solution and oil-HF solution respectively. In systems for extracting gas oil with HF for removing sulfur and carbonforming materials an oil-HF solution or rafiinate is obtained which contains only a small amount of HF. Simultaneously an I-IF-oil solution or extract is obtained which is of very different composition and which contains large amounts of HF. Heretofore HF has been'removed from the separate solutions by separately stripping HF in a stripping zone which is heated at its base and provided with reflux means at its top, cooling the overhead from the stripping zone to a'temperature obtainable by available cooling water and then separating liquid HF from oil in a low temperature settler. Such HF removal means has been found to be satisfactory for separating HF from extract but vexatious problems have been encountered in the separation of HF-from raffinate. Corrosion, gummy tar deposits and coke are encountered in the upper part of the raffinate stripper and such fouling, particularly due to sticky resinous deposits, has been even more aggravating in the cooler for raflinate stripper overhead and most aggravating in the settler for the cooled raffinate overhead. An object of our invention is to prevent such fouling. A further object is to provide an improved method and means for extracting all types of high sulfur gas oils such as virgin gas oils, coke still gas oil, or thermally or catalytically cracked gas oils in order to remove sulfur compounds and coke-forming components, thus producing oils which are highly valuable as catalytic cracking charging stocks and as distillate fuels. A further object is to provide an HF treating and solvent recovery system which will require a minimum capital investment, a minimum operating expense and which at the same time will be of maximum flexibility, utility and effectiveness. Other objects will be apparent as the detailed description of our invention proceeds.

In the preferred embodiment of our invention we countercurrently extract a high sulfur gas oil with liquid HF in the presence of a light hydrocarbon for increasing the effectiveness of the extraction step and facilitating phase separation. Such extraction may be effected in a packed tower at a temperature of about 50 to 150 F. with a solvent ratio in the range of about .05 to 2 volumes, preferably about .5 volume, of HF per volume of gas oil charged. The extract is heated to a temperature in the range of about 400 to 600 F., e. g. about 475 to 500 F. for removing the HF by distillation or stripping, the base of the stripping zone preferably being heated to insure efficient removal of HF and the top of the zone preferably being cooled, for example by introduction of condensed HF thereto for preventing any undue hydrocarbon carry-over. HF is stripped from the rafi'inate in a similar manner except that the temperature in the raflinate stripper may be about F. higher than that of the extract stripper.

In order to avoid fouling in the rafiinate stripper at least a part of the overhead from the exact stripper is introduced directly at an upper point in the raflinate stripper. Where the fouling is due to a corrosive HF-H2O azeotrope the increase in amount of HF which is thus brought about by introduction of extract stripper overhead apparently prevents the HF-HzO ratio from reaching a point which produces excessive corrosion. At the same time the lowering of the temperature in the upper part of the raflinate stripper by the presence of larger amounts of HF reduces the tendency toward coking. Perhaps the outstanding and most important effect of the introduced HF is to prevent accumulations of sticky, gummy deposits of resinous or tarry material at the top of the rafiinate stripper in the line leading from the ralfinate stripper to the rafiinate overhead cooler and in the raffinate overhear settler. In the absence of the added HF these elements became so fouled that they frequently plugged and required a shut-down of the entire unit. The exact cause of the fouling or deposit formation cannot be definitely stated but it appears that the sticky deposits may be due to polymerization or condensation of components in the rafiinate stripper overhead. Regardless of the cause, the presence of the augmented amounts of HF from the extract stripper effectively prevents the fouling either by inhibiting the reaction which leads to the fouling or by providing a composition in which the deposits are soluble. Since the quality of the solvent-free raffinate is not substantially impaired by the introduction of extract stripper overhead into products leaving the top of the rafifinate stripper it would appear that the actual formation of the sticky resinous or tarry materials is actually inhibited.

Since the most troublesome fouling problems occur in the raffinate stripper overhead settler and cooler We may introduce at least a part of the extract stripper overhead directly into said cooler or at any point between the cooler and the rafiinate stripper. Similar results may be obtained by introducing HF from some other source into the rafiinate stripper overhead system but our scheme enables the accomplishment of the desired results and at the same time the elimination of the separate extract stripper overhead settler. In other words, we have materially decreased the investment and operating cost of the.

plicable to HF extraction of viscous oils and in the following example we shall describe the invention as applying to the extraction of a gas oil produced by the cracking of a high sulfur crude. Such a gas oil may be produced by the coking of a West Texas reduced crude at a temperature in the range of about 850 to 1000 F. at a pressure in the range of atmospheric to about 100 p. s. i. and for a time of contact sufficient .to convert the charge into gas, gasoline, gas oil and marketable coke. Alternatively the gas oil may be a cycle oil produced by thermal or catalytic cracking of a charging stock obtained from a West Texas crude. The charge to the cracking or coking step may be admixed with Mid- Continent or other low sulfur crude but such charge should contain a substantial amount of and should preferably predominate in components of high sulfur crude origin. In this example a 55% West Texas reduced crude having an A. P. I. gravity of 19.3, a sulfur content of 2.3% and a boiling range upwards of 500 F. is subjected to a coking operation to produce a Wet gas yield of about 6 weight percent, a market able coke yield of about 13%, a gasoline yield of about 10 volume percent and a coke still gas L oil yield of about 75 volume percent, the latter having an A. P. I. gravity of about 27, a sulfur content of about 1.7%, a burning quality index of about 45, a specific dispersion of about 150,

a refractive index of about 1.498, a cetane num- 1..

her of about 45 and a boiling range of about 400 to 750 F.

The cracked gas oil charge from source I is introduced by pump 1 i and line I 2 to a low point in extraction tower 53. If the charge contains an appreciable amount of moisture it should first be passed through a drying tower or other known means for removing said moisture. If the charge is at a temperature lower than desired extraction temperature it should be preheated by heat exchanger (not shown) to extraction temperature before being introduced at the base of tower l3.

Extraction tower 13 may be packed with 1'- inch carbon rings l4 supported on grid support I5 to insure intimacy of contact with the liquid HF which is introduced at the upper part of the tower through line It. While a countercurrent extraction tower packed with l-inch carbon rings has thus been described it sohuld be understood that any other suitable packing may be employed and that any other known extraction method may be employed instead of a countercurrent tower. The extraction may be for example effected in a batch or multiple batch system. It has been found that best results are obtained on the heavier, more viscous gas oils when a small amount, for example about 2 to 20% or approximately of a light hydrocarbon or mixture of hydrocarbons of the butane to heptane boiling range, for example ,hex-ane, is introduced either by line H below the gas oil inlet or by line is for admixture with the gas 'oil charge. the former giving the best results.

' The amount of solvent may be varied within the fairly wide range of about .05 volume to 2 volumes or more of HF per volume of coke still gas oil charged but from a quality yield standpoint it has been found that good results are obtained with from about .2 to about .5 volume of HF per volume of gas oil charged. Thus using approximately .3 volume of HF per volume of gas oil charged, a raifinate yield of about 81.5% has been obtained with a sulfur content of .48. The extraction may be eifected at ordinary atmospheric temperature or within the range of about 100 to 150 F; and the time of contact may be about 10 to 60 minutes, e. g. about 30 minutes, although shorter times may be employed if greater intimacy of contact :is obtained. The pressure should of course be sufficient to maintain all components in the tower in liquid phase condition.

The extract from the tower is withdrawn through line [9 and heater to extract stripper 2| which may be provided with suitable top cooling or reflux means such for example as cooling coil 22 or reflux introduced through line 23. The extract stripper is provided with conventional heating means 24 which maintain the base of the stripper at a temperature in the range of about 400 to 600, e. g. about 500 F. Auxiliary stripping fluid may be introduced at the base of tower 2| by line 49. Stripped extract is removed from the base of the stripper through line 25 and it may be contacted with bauxite forv decomposing any alkyl fluorides in accordance with conventional practice. The stripped extract has unique properties: in this particular case it contains about 6 weight percent sulfur, it has an A. P. I. gravity of about 7.8, a pour point of +5 F., a viscosity at 210 F. of 53 seconds Saybolt, a furol viscosity at 122 F. of 30, a heat of combustion of 148,500 B. t. 11. per gallon and on ASTM distillation a 10% point at about 510 F., a 50% point at about 688 F. and a 70% point at about 715 F. A similar extract produced by the extraction of total catalytic cycle oil produced by the catalytic cracking of a charging stock containing large amounts of West Texas material had 4.5 weight percent sulfur, an A. P. I. gravity of 1.5, a pour point of 5 F., a viscosity of seconds at 210 F., a furol viscosity at 122 F. of 15, a .heat of combustion of 152,700 B. t. u. per gallon and on ASTM distillation had a 10% point "at about 500 F., .a point at about 640 and a point at about 690 F. For comparisona West Texas virgin gas oil extract had 8.2 weight percent sulfur, an A. P. I. gravity of 10.1, a viscosity of 38 seconds Saybolt at 210 F., a furol viscosity of 13 at 122 F., a heat of combustion of 145,300 B. t. u. per gallon, a pour point of F., and on ASTM distillation had a 10% point at about 530 F., 50% point at about 670 F., and a 70% point at about 720 F.

The raffinate from the extraction tower. I3 is withdrawn through line 26 and heater 2? to raffinate stripper 2B which is provided with a conventional reboiler or heating means 29 at its base and which may also be provided with a cooling means 30 at its top. The base of this stripper is preferably maintained at a temperature in the range of about 450 to 650 (depending on the boiling range of the raihnate), e. g. about 550 F. The stripper raffinate withdrawn through line 31 may be cooled and scrubbed with caustic in a scrubbing system (not shown) or treated with bauxite to remove any residual amounts of HF, and such stripped rafiinate, which may constitute about 81.5 volume percent of the gas oil charged, may have an API gravity of about 32, a sulfur content of less than .5, a burning quality index upwards of '75, a specific dispersion of about 130, a refractive index of about 1.481, a cetane number of about 51 and an ASTM boiling range between the 10% and 90% point which is not materially different from that of the charging stock.

The burning quality index is a measure of the carbon or deposit forming constituents of a distillate fuel and it is determined by a test on a Coleman model 82113 space heater. The test involves determining the weight of total burner deposits when 10 gallons of fuel are burned at the rate of .3 gallon per hour employing .06-inch of Water draft. The theoretically perfect fuel would, of course, give no burner deposits; such a fuel is arbitrarily defined as having a burning quality index or BQI of 100. A good commercial distillate fuel may give a burner deposit of about grams and thus have a BQI of 60. Fuels having a B'QI of less than 60 are unsatisfactory on many types of heaters and the remarkable improvement in BQI effected by the HF extraction of coke still gas oil is of enormous commercial importance. Surprisingly enough the BQI of a virgin Mid-Continent distillate fuel is not improved by HF extraction while the HF extraction of a high sulfur coke still gas oil as hereinabove described results in a fuel which is even superior to fuels heretofore produced from low sulfur Mid-Continent gas oil.

The overhead from rafiinate stripper 28 is introduced by line 32 through cooler 33 to settler 34 which operates at as low a temperature as can be obtained by available cooling water. Heretofore much difficulty has been encountered in this portion of the extraction system due to corrosion in the upper part of the rafliniate stripper and the accumulation of deposits from the top of the rafiinate stripper to the settler. Just What causes the corrosion and the deposits is difllcult to understand but pilot plant demonsrations have shown that the fouling of equipment in this portion of the system is a serious problem because the lines, cooler and/or settler become so plugged as to require a shut-down of the entire plant. We have solved this fouling problem and at the same time markedly reduced the investment and operating cost of the plant by discharging at least a part of the overhead from extract stripper 2i through line 35 and branch line 36 into the upper part of the rafiinate stripper. At least a part of the extract stripper overhead may also be introduced through line 31 to a point in line 32 in advance of cooler 33. If desired at least a part of the extract stripper overhead may be introduced through line 38 and cooler 39 directly to settler 36 or to the line entering the settler. Since the settler operation appears to be subject to severest fouling advantageous results may be obtained by introducing all of the extract stripper overhead through line 38 and cooler 39 to the settler. However for maximum trouble-free operation we prefer to introduce all or a major portion of the extract stripper overhead through line 36 to the upper part of the stripper and/or to introduce at least a portion through line 31 in advance of cooler 33. Extensive pilot plant operations have shown that by thus combining the extract stripper overhead with overhead produced in the rafiinate stripper, trouble-free operation may be obtained in the extraction unit over along period of time.

The liquid HF which separates as a bottom layer in settler 3G is withdrawn through line 46 and returned by pump "5i to line it for introduction to the extraction tower, any make-up HF being supplied from source 412. When small amounts, e. g. less than about .2 volume of HF, are employed in the extraction step it may be desirable to introduce a part of the HF through line 23 at the upper part of extract stripper 21; such HF acts as reflux in stripper 2i and also supplies the necessary HF for introduction into the ramnate stripper and recovery system. Ordinarily the amount of HF in the raffinate entering the raffinate stripper is only about .1 to .6 weight percent. This does not provide suificient HF in the top of the raffinate stripper in the succeeding portion of the system for preventing corrosion and the accumulation of deposits. In accordance with the operation hereinabove described however the HF concentration at the top of the raidnate stripper is increased many fold and a two to five fold increase materially improves the operation of the system.

The upper light hydrocarbon layer in settler 34 flows over baflie 43 and is withdrawn through line 44 by pump 45. At least a portion of this stream may be returned by line 46 which leads to lines ll and I8. A portion of the light hydrocarbon may also be pumped through line 49 into the bottom of the extract stripper to aid in removing the HF from the extract. Some or all of the light hydrocarbon thus withdrawn may be removed from the system through line 41 and the removed light hydrocarbons may be replaced by fresh light hydrocarbons introduced through source 48. Any gases formed in the system may be withdrawn through line 49. The gases and/ or the light hydrocarbons withdrawn from the system may be scrubbed with an absorber material for recovering HF contained therein and the recovered HF may be returned to the system.

While we have described in considerable detail a specific example of our invention it should be understood that various alternative systems and operating conditions will be apparent from the above description to those skilled in the art.

We claim:

1. The method of preventing the fouling of equipment employed in a system for treating an oil with HF wherein one fraction is obtained which is soluble in HF and another fraction is obtained which is insoluble in HF and which contains only a small amount of dissolved HF, which method comprises stripping HF from the soluble fraction in a first stripping zone, stripping HF from the insoluble fraction in .a secondstripping zone, cooling and condensing overhead materials produced in the operation of both stripping zones, and introducing at least a part of the overhead material from the first stripping zone into the upper part of the second stripping zone before separating HF from the condensed materials.

2. The method of preventing the fouling of equipment employed in .a. system for treating an oil with .HF wherein one fraction is obtained which is soluble in HF and another fraction is obtained which is insoluble inI-lJF' and which contains only a small amount of dissolved HF, which method comprisesstripping HF from the soluble fraction in a first stripping zone, stripping HF 15 from the insoluble fraction in a second stripping zone, cooling and condensing overhead materials produced in the operation of both stripping zones, separately condensing at least part of theoverhead from the first stripping zone and introducing the resultant condensate directly into a zone wherein HF and condensed overhead materials derivedfrom said second stripping zone are separated into distinct liquid phases by settling.

3. The method of preventing the .fouling of equipment employed in a system for treating an oil with HF wherein one fraction is obtained which is soluble in HF and another fraction is obtained which is insoluble in FF and which constripping zone and before the last-named material is cooled.

WALDEMAR R. IERTWIG. JAMES D. BUSHNELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,320,629 Matuszak June 1, 1943 2,339,786 Larsen et al Jan. 25, 1944 2,378,762 Frey June 19, 1945 2,425,559 Passino et a1 Aug. 12, 1947 2,427,009 Lien et a1 Sept. 9, 1947 2,449,463 Evering et al Sept. 18, 1948 2,450,588 Evering et a1 Oct. 5, 1948 2,479,238 Holm et a1 Aug. 16, 1949 

1. THE METHOD OF PREVENTING THE FOULING OF EQUIPMENT EMPLOYED IN A SYSTEM FOR TREATING AN OIL WITH HF WHEREIN ONE FRACTION IS OBTAINED WHICH IS SOLUBLE IN HF AND ANOTHER FRACTION IS OBTAINED WHICH IS INSOLUBLE IN HF AND WHICH CONTAINS ONLY A SMALL AMOUNT OF DISSOLVED HF, WHICH METHOD COMPRISES STRIPPING HF FROM THE SOLUBLE FRACTION IN A FIRST STRIPPING ZONE, STRIPPING HF FROM THE INSOLUBLE FRACTION IN A SECOND STRIPPING ZONE, COOLING AND CONDENSING OVERHEAD MATERIALS PRODUCED IN THE OPERATION OF BOTH STRIPPING ZONES, AND INTRODUCING AT LEAST A PART OF THE OVERHEAD 